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Enhancement Optimized MAC Protocol for Medical. Applications. Boufedah Badissi Azzouz1, Benmohamed Mohamed1, Babouri Abdesselam2 , Claire ...

Enhancement Optimized MAC Protocol for Medical Applications Boufedah Badissi Azzouz1, Benmohamed Mohamed1, Babouri Abdesselam2 , Claire goursaud3 and Florin Hutu3 1

LIRE Laboratory, University of Constantine, Nouvelle ville Ali Mendjli BP67A, Constantine, Algeria 2 LGEG Laboratory, university of Guelma BP401, 24000, Guelma, Algeria 3 CITI Laboratory, INSA Lyon Domaine Scientifique de la Doua, Villeurbanne, France

Abstract— Growth of elderly population induces the increasing demands for high-quality healthcare services, wireless body area networks (WBANs) has emerged as a promising solution for monitoring of patients vital life signs parameters. Reliability and extending the lifetime are considered amongst the important and challenging issues in WBANs. The standard IEEE 802.15.4 is considered as the most used MAC protocol for medical sensor body area networks, owing to its low-power, low data rate and low-cost features. In this paper, we propose an enhancement optimized MAC protocol based on IEEE 802.15.4 dubbed EOMAC. The proposed protocol aims to enhance the reliability and to prolong the lifetime of the network, by reducing energy consumption. Index Terms— IEEE802.15.4, Reliability, GTS, Superframe, NS.




I. INTRODUCTION The last decade has seen rapid growth in elderly people especially in developed countries, which lead to a new challenge to furnish good life-quality for population. In this context, integration of the latest technologies of sensors and telecommunications which permit permanent monitoring of patients, is considered as one of the hopeful applications. Current evolution in low-power integrated circuits, wireless communications, and physiological sensing have led to the development of miniature, low cost, low power, intelligent, multi-functional sensor nodes, capable of processing information locally and communicate in short distances. These sensors in or around human body can communicate between them or/and with a central device (sink) forming a scheme dubbed Wireless Body Area Network (WBAN). A WBAN is an instance that enables continuous parameters monitoring of the patient's vital signs in everyday life, without confining their normal activities. Using WBAN is more reliable for medical personal than during stays in the hospital because medical data are acquired periodically for long time intervals. The continual observation and monitoring is the real purpose for staying in the hospital which become extremely costly. As a consequence, the center of interest of health policy has shifted away from the provision of acute care toward preventive care outside the hospital [1]. In a healthcare monitoring system, data transmission reliability is extremely important because human life is at stake. In WBANs, most of devices are powered by batteries, so the main consideration is to prolong the lifetime of

networks. At the medium access control (MAC) sublayer the allocation of the channel resources between different users will take place. In this level, the transmission of measured vital biomedical data upon wireless channel requires an effective and reliable protocol. IEEE 802.15.4 MAC protocol is one of the most widely used protocols for wireless personal area networks (WPANs), which is able for applications to connect WBAN to larger networks. It is considered to be a good applicant owing to its low-cost and low-power characteristics, but it couldn't guarantee the reliability [2]. In case of star topology with heterogeneous devices, the network will be out of service when the first sensor depletes its energy. The Enhancement Optimized MAC protocol, dubbed EOMAC was proposed to address these challenges. In this work, we present a WBAN that consists of six heterogenuous medical sensors carried by a person, extract physiological data from the body and then transmit them to a coordinator sensor (sink) in the same local. The coordinator connected to the home PC, which is connected through internet with remote medical personal. The rest of the paper is organized as follows: previous related work is discussed in the next section. In section-III, we present an overview of the IEEE 802.15.4 standard. The detail of the Enhancement Optimized MAC protocol proposed is highlighted in the section-IV. Sections V and VI, report the simulation settings and simulation results, respectively. Finally, section VII concludes the paper. II. RELATED WORK Performance evaluation of IEEE 802.15.4 and/or Zigbee protocols are presented in divers works, most of them are based on simulations [3],[4] or an analytical models [5],[6]. In reference [7], the author's present the performances of the ZigBee based sensor network for patient monitoring through NS2 simulator. The performances are measured in terms of packet delivery ratio (PDR), average delay, throughput and energy consumption. The obtained results can be used to choose the appropriate nodes density, data transmission rate, amount of data to transmit and duration of communication. The allocation method to reduce the waste of bandwidth using the GTS (Guaranteed Time Slot) mechanism was addressed in References [8] and [9]. The first furnishes a mechanism to allow more devices in one time slot. The last divides the CFP (Contention Free Period) period into 16 equal time slots to attribute the time slot to reduce the wasted bandwidth specially

for low data rates sensors, its disadvantage is to rival with other device in the CAP (Contention Access Period) period to have the channel access. In Reference [10], a new mechanism to enhance the performance and utilization by using CFP is presented, the work aimed to cope with the competitor access to the radio channel using GTS in the CFP period. An algorithm to optimize a GTS allocation is proposed in [11], the purpose is to enhance reliability and bandwidth utilization in IEEE 802.15.4-based Wireless Body Area Networks. In [12], the author proposes a linear programming model which optimizes the location and number of relays, in order to prolong the WBAN lifetime. Several works have examined the performance reinforcement obtained using single hop [13] and multi-hop schemes [14],[15]. The effect of adding a relay to the network of body sensors to reduce energy consumption of sensor nodes when transmitting data to the sink was presented in [16], [17]. III. IEEE 802.15.4 MAC OVERVIEW IEEE 802.15.4 standard defines the physical layer and the MAC sub-layer for Low-Rate Wireless Personal Area Networks (LR-WPANs) which contends on short-range operation, low-data-rate, energy-efficiency and low-cost [18]. There are two types of nodes. A Full Function Device (FFD) can operate as PAN coordinator, ordinary coordinator or an end device. A Reduced Function Device (RFD) can operate only as an end device and then communicate only with its associated FFD. The standard may operate in the star topology and the peer-to-peer topology, as illustrated in Figure.1.

Fig.1. Star and peer to peer topology examples In both topologies, the standard takes in charge two operational modes that may be selected by the PAN coordinator. Beacon enabled mode and non-beacon enabled mode. In non-beacon enabled mode, no superframe and no synchronization slot is available. There are two kinds of superframe structure defined in the standard in case of beacon enabled mode. One is for one-hop star topology as illustrated in Figure2, and the second is for muti-hop network as shown in Figure3.

Fig.2. An example of the superframe structure (star)

In star topology, the superframe consists of active and inactive periods. The active period is divided into 16 equal duration slots and it consists of a beacon, a contention access period (CAP) and a contention free period (CFP).

Fig 3: The relationship between incoming and outcoming beacons.

Any device wants to communicate during the contention access period (CAP) between two beacons competes with other devices using a slotted CSMA-CA or ALOHA mechanism, as appropriate [18]. The beacon interval (BI) is determined by the beacon order parameter (BO) and the superframe duration (SD) by the superframe order (SO) as defined by the following equations. BI=aBaseSuperframeDuration*2BO for 0

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